1. Field of the Invention
The present invention relates to a magnetic head having an enhanced bonding strength between a lead wire and a conductive member and having improved reliability, in which the lead wire leads from a head element of a thin film magnetic head and the like, and the conductive member exchanges electrical signals with the head element.
2. Description of the Related Art
As shown in FIG. 9, the front portion of a flexure 2 is cut away in the form of an approximately U-shape to form a small portion 2a, and four conductive patterns 3 composed of copper and coated with gold by plating thereon are formed on the surface of the flexure 2 coated by a polyimide resin.
End portions 3a of the conductive patterns 3 are formed so as to broaden and are lined up on the small portion 2a.
A slider 1 in the form of a rectangular parallelepiped is fixed by bonding at a bottom surface 1b thereof on the small portion 2a of the flexure 2 so that the end portions 3a of the conductive patterns 3 oppose a side wall 1a of the slider 1.
As shown in FIG. 10 and FIG. 11, the side wall 1a of the slider 1 has a head element 7 for writing on and/or reading from a magnetic recording medium, and four lead wires 8, two for writing and two for reading, lead from the head element 7. An edge 8a of each lead wire 8 having a wider area in an approximately rectangular form is formed in the vicinity of the surface of the flexure 2. Individual edges 8a of the four lead wires 8 are disposed so as to oppose the corresponding end portions 3a of the conductive patterns 3 in the vicinity thereof.
As shown in FIG. 11, a bump 10 composed of nickel or the like is provided on the edge 8a of the lead wire 8. The bump 10 is composed of a cylindrical pillar portion 10a having the bottom surface contacting nearly the entire edge 8a of the lead wire 8 and an umbrella-like portion 10b expanding at the front edge of the pillar portion 10a.
The umbrella-like portion 10b of the bump 10 has an excavated top at the top of approximately hemispherical form, and a round area at the center of the umbrella-like portion 10b is to be used as a contact area 10d of the bump 10.
The contact area 10d of the bump 10 has an inclined portion 10f at the periphery thereof and is recessed into the spherical portion 10e of the umbrella-like portion 10b.
A protective layer 9 composed of alumina covers the head element 7, the lead wires 8, and the surfaces of the pillar portions 10a and the spherical portions 10e of the bumps 10 on the side wall 1a, and is formed so as to be flat. The surface of the contact area 10d of the bump 10 is exposed from the protective layer 9, and is recessed from the level of the surface of the protective layer 9 since the inclined portion 10f exists at the boundary of the protective layer 9.
The contact area 10d of the bump 10 exposed from the protective layer 9 is adjacent to the surface of the flexure 2.
In a polishing process for polishing the protective layer 9 so as to expose the contact area 10d of the bump 10, the form of the umbrella-like portion 10b of the bump 10 as described above is formed by polishing the top of the approximately hemispherical umbrella-like portion 10b of the bump 10 together with the protective layer 9.
In the polishing process, the bump 10 composed of a metal, such as nickel, is easily polished since the bump 10 is softer than the protective layer 9 composed of alumina, so that the contact area 10d of the bump 10 exposed from the protective layer 9 has the inclined portion 10f at the boundary of the protective layer 9 and is recessed from the level of the surface of the protective layer 9.
Four rectangular pads 11 composed of thin gold films or the like cover the surfaces of the individual contact areas 10d of the four bumps 10 exposed from the protective layer 9, and are disposed so as to oppose the corresponding end portions 3a of the conductive pattern 3 on the surface of the flexure 2 adjacent to each other.
The pads 11 includes a recessed portion 11a covering the surface of the contact area 10d of the bump 10 and an inclined portion 11f overlaying an inclined portion 10f of the bump 10 from the contact area 10d thereof to the surface of the protective layer 9.
Since the contact area 10d of the bump 10 is adjacent to the surface of the flexure 2, the recessed portion 11a of the pad 11 and the inclined portion 11f thereof are also adjacent to the end portion 3a of the conductive pattern 3 formed on the surface of the flexure 2.
At an angular portion 12 at which the side wall 1a of the slider 1 and the surface of the flexure 2 contact each other, an approximately spherical bonding member 13, composed of gold or the like, is joined in contact with the recessed portion 11a of the pad 11 and the end portion 3a of the conductive pattern 3, so that the pad 11 and the conductive pattern 3 are connected to each other. On the surface of the approximately spherical bonding member 13, a protruding residual portion 13a remains.
As shown in FIGS. 12 and 13, there is a conventional example in which wire 15 is used as the bonding member, and in which an edge portion 15a of the wire 15 is bonded to the recessed portion 11a of the pad 11, and the other edge portion 15b of the wire 15 is bonded to the end portion 3a of the conductive pattern 3.
In the magnetic head described above, the surface of the slider 1 is disposed so as to oppose the magnetic recording surface of the magnetic disc, and the slider 1 fixed to the flexure 2 is raised at a predetermined distance over the magnetic recording surface of the magnetic disc during an operation of the magnetic hard disc. The head element 7 is connected to an external circuit through the lead wires 8, the bumps 10, and the conductive patterns bonded by the bonding members to the bumps 10 via the pads 11 so as to perform magnetic writing on and reading from the magnetic disc by transmission of electric signals of electric circuits from the head element 7 to the external circuit.
In a bonding process for bonding the pad 11 and the conductive pattern 3 by using the spherical bonding member 13, as shown in FIG. 14, a front edge of a fine gold wire 17 drawn from a capillary 16 for bonding is melted by discharging, whereby the spherical bonding member 13 is formed. When the bonding member 13 contacts the recessed portion 11a of the pad 11 and the surface of the end portion 3a of the conductive pattern 3, ultrasonic vibration is imparted to the bonding member 13, and the bonding member 13 is bonded to the pad 11 and to the end portion 3a of the conductive pattern 3 by ultrasonic welding.
In this case, since the pad 11 has the recessed portion 11a adjacent to the end portion 3a of the conductive pattern 3 in the conventional magnetic head, depending on the size of the spherical bonding member 13, the bonding member 13 may be bonded to the end portion 3a of the conductive pattern 3 and an angular portion of the inclined portion 11f of the pad 11, as shown in FIG. 15. Consequently, there is a problem in that contact defects between the bonding member 13 and the pad 11 may occur.
When the spherical bonding member 13 rotates along the inclined portion 11f of the pad 11, as shown in FIG. 16, the bonding member 13 is placed at the pad 11 side and is raised from the end portion 3a of the conductive pattern 3, so that there is a problem in that contact failure with the conductive pattern 3 may occur.
When the bonding member for bonding the pad 11 and the conductive pattern 3 is the wire 15, as shown in FIGS. 12 and 13, the front edge portion 15a of the wire 15 is contacted to the recessed portion 11a of the pad 11, and then the front edge portion 15a of the wire 15 and the recessed portion 11a of the pad 11 are bonded by ultrasonic vibration imparted to the wire 15. Subsequently, after forming a bending portion 15c in the wire 15, the other edge portion 15b of the wire 15 is contacted to the end portion 3a of the conductive pattern 3, and then ultrasonic vibration is imparted to the wire 15, whereby the other edge portion 15b of the wire 15 and the end portion 3a of the conductive pattern 3 are bonded to each other.
In this case, since the pad 11 has the inclined portion 11f in a conventional magnetic head, as shown in FIG. 17, the front edge portion 15a of the wire 15 contacts the angular portion of the inclined portion 11f of the pad 11 and is raised from the pad 11. Consequently, the bonding area between the wire 15 and the pad 11 is small, and contact defects occur therebetween.